Assembly for sequentially percutaneously applying an electrode and an anesthetic to tissue

ABSTRACT

An assembly that consist of a cannula; an electrode and a syringe. The cannula has a hub that defines a set of adjacent bores. A first proximal bore receives the head of the electrode. A second bore receives the head of the syringe. The cannula has a stop that limits the extent to which the electrode can be inserted in the proximal bore. When the syringe is inserted in the cannula hub, the syringe is inserted beyond the stop. The syringe presses against an adjacent surface that defines the second bore to form a seal between the cannula and the syringe.

FIELD OF THE INVENTION

This invention relates generally to an assembly for percutaneouslyapplying an electrode and fluid to tissue. The assembly of thisinvention includes features that facilitate the rapid and precisepositioning of the electrode.

BACKGROUND OF THE INVENTION

In some medical procedures it is desirable to both apply an electricalcurrent and a fluid to the same target location within the body of thepatient. One such procedure in which these steps are performed is anerve ablation procedure. In a nerve ablation procedure, the nervesubjected to the procedure is ablated, essentially removed. As a resultof the ablation process, the nerve no longer functions as a carrier forneurological signals. A nerve ablation is performed in some situationswhen the patient's neurological system continually transmits signals tothe brain that provide the perception that that a limb or other portionof the patient is in pain. To eliminate the transmission of thesesignals, it is a known practice to ablate the nerves that continuallytransmit the pain signals to the brain.

A first step of a nerve ablation procedure is to insert a cannula intothe patient. The distal end of the cannula is located in close proximityto the nerve targeted for the ablation procedure. An electrode isinserted in the cannula. A low power current, called a stimulatingcurrent, is then sourced from the electrode to the tissue adjacent theend of the cannula. The reaction of the patient to this current ismonitored. More specifically, the practitioner monitors the reaction ofthe patient to determine how close the electrode is to the nerve thatshould be ablated. As part of this process, the cannula, with theelectrode still inside, is typically repositioned. Once it is determinedthat the cannula and electrode are correctly positioned, the electrodeis removed. The distal end of a syringe filled with a fluid,specifically an anesthetic, is inserted in the hub located at theproximal end of the cannula. The anesthetic is introduced through thecannula to the nerve and tissue surrounding the nerve. The syringe iswithdrawn and the electrode reinserted into the cannula. A current isagain sourced from the electrode. This current, referred to as anablating current, is at a much higher level than stimulating current.Specifically, the ablating current is at level at which, when applied tothe nerve, causes the ablation of the nerve. During this process theanesthetic reduces, if not completely blocks, the pain signals generatedduring the application of this relatively high current to the tissue.

As mentioned above, the cannula employed in this type of assemblyincludes a hub. The hub has a relatively large diameter bore in which acomplementary head of the electrode and head of syringe arealternatingly fitted. A problem with many known versions of theseassemblies is that it has proven difficult to, when the electrode isreinserted into the cannula, to perform the ablation step, position thedistal end of the electrode so it extends the same distance out of thecannula as it did during the stimulating step. Having to take the timeto so precisely reposition the electrode can add to the overall time ittakes to perform a nerve ablation procedure.

SUMMARY OF THE INVENTION

This invention relates to a new and useful assembly for interchangeablyinserting an electrode into and coupling a syringe to a cannula. Theassembly of this invention is designed so that each time the electrodeis inserted in the cannula, the distal end of the electrode extends outof the cannula essentially the same distance as it did during theprevious insertions.

A further feature of this invention that essentially a zero force isemployed to insert the electrode into or withdraw the electrode from thecannula. While essential zero force is employed to insert or withdrawthe electrode, the assembly of this invention includes a means forreleasably holding the electrode to the cannula.

In one version of this invention, the cannula includes a hub that isformed with a number of contiguous bores. The bores form a through pathto the tube portion of the cannula that extends distally from the hub.The cannula is further formed so that the cannula has a stop. In someversions of the invention, a lip or tabs that extend outwardly aroundthe open end of the proximal most bore function as the stop. In someversions of the invention, the stop projects into at least one of thebores. In some versions of this invention, this stop is a step thatforms the transition between two contiguous bores in the cannula. Thecannula is further formed so that the proximal bore with which the stopis formed is dimensioned to facilitate the slip fitting of the electrodeinto the bore. The electrode is slip fitted into the bore until theelectrode abuts the stop.

One or more of the bores proximal to the stop is dimensioned to receivethe head of the syringe. This bore is located distal to the proximal endbore, the bore dimensioned to receive the head of the electrode.

A further feature of the invention is that cannula is formed with afeature configured to releasably engage the electrode. Typically, thisfeature is disposed in the proximally located bore, the bore in whichthe electrode is disposed. In many versions of the invention theproximal bore has a constant diameter. In many versions of theinvention, the feature configured to releasably engage the electrodeprojects into the proximal bore.

In another version of the invention, the cannula has two proximal endbores. A first one of the bores is dimensioned to receive the head ofthe electrode. A second one of the proximal end bores is dimensioned toreceive the head of the syringe. Both the electrode and syringe can besimultaneously removably attached to the cannula of this version of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the claims. The aboveand further features and advantages of this invention are understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 depicts the components of the assembly of this invention;

FIG. 2 is a cross sectional view of the proximal portion of the cannulaof this invention;

FIG. 3 is a plan view of the distal end face of the head of an electrodeof this invention.

FIG. 4 is a perspective view of the insertion of an electrode into thecannula;

FIG. 5 is a cross sectional view of the electrode locked in the cannula;

FIG. 5A is a an enlarged cross sectional view of the distal ends of thecannula and electrode;

FIG. 6 is cross sectional view of the syringe coupled to the cannula;

FIG. 7 is a cross sectional view of how in an alternative assembly ofthis invention, the electrode seats in the cannula; and

FIG. 8 is a cross sectional view of an alternative cannula of thisinvention.

DETAILED DESCRIPTION

FIG. 1 depicts the basic components of an assembly 30 of this invention.These components include a cannula 32. Cannula 32 is insertedpercutaneously into the patient to provide a portal that opens into thespace adjacent the tissue against which the current is to be applied. Anelectrode 70, also part of assembly 30, is inserted into the cannula 32.The electrode 70 is the device that sources the current to the tissue.Assembly 30 also includes a syringe 90. Syringe 90 is the source offluid that is introduced into the tissue. This fluid is typically ananesthetic.

As seen by reference to FIGS. 1 and 2, cannula 32 includes a hub 34 fromwhich a tube 60 extends distally forward. (“Distal” is to mean away fromthe practitioner using assembly 30, towards the percutaneous target siteto which the assembly is applied. “Proximally” is understood to meantowards the practitioner holding the assembly, away from the site towhich the assembly 30 is applied.) Hub 34 is dimensioned to be heldbetween two fingers. The hub 34 is formed from a soft plastic such as anABS plastic or Nylon, or other material that has a degree of flexibilityor compliancy. Hub 34 has a body 36 that, while generally circular incross section, has an outer diameter that extending from the proximal todistal ends of the body, decreases. A number of parallel fins 38 extendoutwardly from the hub body 36. The outer surfaces of the fins 38 arethe portions of the cannula 32 held by the practitioner to position thecannula. At the most proximal end of the body 36 two diametricallyopposed tabs 37 (one identified) project radially outwardly. There is aseparation between tabs 37 and the proximalmost fins 38.

Hub body 36 is further formed to have a number of contiguous bores thatcollectively form a through path that extend proximally to distallyalong the longitudinal axis of the body. A proximal bore 40 extendsdistally forward from the proximal end of the body 36. The hub 34 isshaped so that the proximal bore 40 has a diameter that is constantalong the length of the bore. Cannula 32 is further formed so that atleast one, if not plural, ribs 42 project radially inwardly from theinner circular wall 39 of the hub 34 that defines bore 40. While notapparent from the drawings, in the described version of the inventionthere are two ribs 42, the ribs being arcuately spaced apart from eachother. In this version of the invention, each rib subtends an arc ofbetween 30 and 90°. The opposed sides of the ribs are thus spacedbetween 90 and 150° from each other. It is a further feature of cannula32 that the ribs 42 terminate at a location that is spaced proximallyaway from the distal end of the proximal bore 40. In the illustratedversion of the invention proximal end of each rib 42 is located distallyforward of the proximal end opening into the bore 40.

While not identified, it can be seen that each rib 42 has a distallydirected face. Two wing faces taper proximally away from the opposedsides of the distally directed face. A side surface extends proximallyaway from the free end of each wing face. A rear face extends betweenthe spaced apart side faces.

Proximal bore 40 opens into first middle bore 50. Hub body 36 is shapedso that the proximal end of middle bore 50 is smaller in diameter thanthe adjacent distal end of proximal 40. In some versions of theinvention, the diameter of the proximal end of middle bore 50 isapproximately 0.2 to 1.5 mm less than the diameter of proximal bore 40.In most versions of the invention the difference in the diameters of thetwo bores 40 and 50 is at least 0.6 mm. This difference in bore diameterwith the hub 32 means that, within the hub body, there is a step 46.Step 46 defines the distal end of proximal bore 40 and extends radiallyinwardly from the outer perimeter of the proximal bore. The step 46 hasan inner perimeter that defines the outer perimeter of the proximalsection of distal bore 50. The width across a cross sectional slice ofstep 46 is one-half the difference in diameters between proximal bore 40and the adjacent section of distal bore 50. Hub 34 is further formed sothe inner wall 49 that defines middle bore 50 has a number of notches 48(one identified) that extend outwardly from the inner wall of the hubthat defines bore 50. Each notch 48 extends proximally from a locationspaced distally from step 46 to the step. Each notch 48 is tapered inthat the depth of the notch relative to the arcuately adjacent extendsdistally forward.

The hub body 36 is formed so that, extending distally forward of step46, the diameter of first middle bore 50 gradually decreases. The distalend of the first middle bore 50 opens into a second middle bore 52.Second middle bore 52, like first middle bore 50 is tapered. Thedifference between the two bores is that the taper of second middle bore52 is more pronounced than the taper of first middle bore 50. The secondmiddle bore 52 opens into a distal bore 54. Distal bore 54 has aconstant diameter and forms an opening at the distal end of hub 34.

Cannula tube 60, as implied by its name, is a tubular shaped member.Often tube 60 is formed from stainless steel. In many versions of theinvention, tube 60 has an outer diameter that is 2.0 mm or less and moreoften 1.3 mm or less. A lumen 62 extends axially through the tube.Cannula 32 is assembled so that distal bore 54 opens into tube lumen 62.Typically the hub distal bore 54 has a diameter that is equal to or lessthan the diameter of tube lumen 62. While not illustrated in versions ofthe invention in which tube 60 is formed from conductive material anelectrical insulator is disposed over most if not all of the tube. Insome constructions of the invention, there is no insulator over thedistal end tip of the tube 60. In the version of the tube 60 seen inFIG. 5A, the distal end of face of the tube is beveled. This facilitatesthe insertion of tube 60 through tissue.

Electrode 70, now described by reference to FIGS. 3 and 4, is part of anassembly that includes a cable 72. Cable 72 extends to a console (notillustrated) that serves as the source of current that is sourced to thepatient using assembly 30 of this invention. One such console is theApplicant's Stryker MULTIGEN Console available from Stryker Instrumentsof Kalamazoo, Mich., United States. The structure of the console andcable 72 are not part of the present invention.

The cable 72 extends to a trunk 71 that can be considered the proximalmost portion of the invention forming the electrode assembly 70. Trunk73 is formed from a rigid plastic such as polyaryletherketone. Trunk 73is cylindrical in shape. Electrode assembly 70 includes a head 74 thatis integral with and extends distally forward from trunk 70. The head 74is cylindrical in shape and has a diameter less than that of the trunk70. Assembly 30 is constructed so that the outer diameter of electrodehead 74 is approximately 0.1 mm less than the diameter of cannulaproximal bore 40. This allows the close slip fitting of the electrodehead 74 in the cannula bore 40. Head 74 is further formed to have aminimum diameter that is at least 0.2 mm greater than the maximumdiameter of the cannula middle bore 50. This bore diameter is understoodto be at least the diameter of the inner perimeter of step 46.

The electrode 70 is further formed so that at least one ear 76 extendsradially outwardly from the outer cylindrical wall of the head.Electrode 70 is shaped so that when the head 74 is inserted in cannulaproximal bore 40, the ear 76 will located forward of hub ribs 42. In theillustrated version of the invention, the electrode assembly 70 includesplural ears 76. Ears 76 are arcuately dimensioned and spaced apart fromeach other so that during the process of coupling the electrode assemblyto the cannula each ear 76 can move between the annular gap in hub bore40 between arcuately adjacent ribs 42. Head 74 is further understood tohave a distally directed face 78.

An elongated conductive shaft 80 extends forward from the distal endface 78 of head 78. Shaft 80 is formed from electrically conductivematerial and is the actual component of the electrode 70 from whichcurrent is sourced and to which current is sunk. The components formingassembly 30 are designed so that when electrode 70 is properly seated inthe cannula 32, the distal end tip of shaft 80 protrudes forward a shortdistance from the distal end opening of cannula tube 60. Not illustratedand not part of the application are the conductors internal to trunk 73and head 74 that provide the electrical connection between a conductorinternal to cable 72 and shaft 80.

Syringe 90, as seen in FIGS. 1 and 6, has an elongated tube like trunkor main section 94. Tabs 92 extend outwardly from opposed sides of thetrunk 94 adjacent the proximal end of the trunk. A head 96 projectsforward from trunk 94. The syringe 90 is formed so that as the headextends distally the outer diameter of the head 96 decreases. Moreparticularly, the components forming assembly 30 are designed so thatthe distal most portion of syringe head will press against the innerwall of the cannula that defines the middle bore 50 and the portion ofthe syringe proximal to this section will be spaced from the inner wall39 of cannula hub that defines proximal bore 40.

A collar 98 also extends forward from the distal end of syringe trunk94. Collar 98 is circular in cross section surrounds and is radiallyspaced away from head 96. Collar 98 is formed with grooves 99 thatextend outwardly from the inner surface of the collar. Grooves 99 extendin a helical pattern through collar 98.

A plunger 102 is slidably moved through and removed from the opening atthe distal end of the syringe trunk.

Assembly 30 of this invention can be used for a nerve ablationprocedure. When the assembly 30 is so used, cannula 32 is first insertedinto the patient to provide a portal to a site that is adjacent thenerve to be ablated. During the cannula insertion process, a stylet istypically disposed in the bores and lumen that extend axially throughthe cannula (stylet not illustrated). The stylet provides structurestrength to the cannula, especially tube 60. Once the cannula is soinserted, the stylet is removed.

The electrode 70 is then coupled to the cannula 32. In this process, theassembly shaft 80 is feed through proximal bore 40, middle bore 50 anddistal bore 54 so as to extend in and through the cannula tube lumen 62.In this process, owing to the dimensioning of the components, thepractitioner does not exert a relatively large force that would beneeded overcome a friction (compression) force that holds the electrodehead 74 static in the proximal bore 40. During the process of seatingthe cannula, the cannula 32 and electrode assembly 70 have a rotationalorientation relative to each other that the electrode ears 76 can slidebetween the cannula ribs 42. The electrode assembly 70 is inserted intothe cannula 34 until, owing to the above of the assembly components,electrode head face 78 seats against step 46 internal to the cannula.Step 46 functions as a stop that prevents further advancement of theelectrode 70. Once assembly 30 is in this state, the distal end 81 ofthe electrode conductive shaft 80 projects out of cannula tube 60 asseen in FIG. 5A.

Once the electrode 70 is so positioned, the assembly head 74 is rotated.The head is rotated so that each electrode rib 76 is in registrationwith and distal an associated one of the cannula ribs 42 as seen in FIG.5. This positioning of the electrode 70 is considered to be the lockingof the electrode assembly in place.

A low current, typically approximately 6 mAmps, is sourced to/sunk fromthe electrode. More particularly, this current is sourced from the tipof shaft 80 that extends out of cannula tube 60. The described versionof the invention is a monopolar electrosurgical system. The currentflows between the tip of electrode shaft 80 and a ground pad that isoften adhesively secured to the patient. The ground pad is not part ofthe present invention and is not illustrated.

The practitioner monitors the reaction of the patient to this tissue.Based on the patient's reactions, the practitioner, by manipulating theexposed portion of the cannula 32, positions the cannula and electrodeso that the exposed distal end of the electrode shaft 80 is in closeproximity to the tissue to be ablated. Once this portion of theprocedure is performed, the practitioner withdraws the electrodeassembly 70. The withdrawal starts with the rotation of the electrodeassembly so that ears 76 are rotated out of registration with cannularibs 42. This is considered moving the electrode assembly from thelocked state to the load state. Once the electrode 70 is in the loadstate, the electrode is withdrawn from the catheter 32.

The syringe 90 is filled with anesthetic. The syringe is then fittedcoupled to the cannula 32. This process involves fitting the syringeover the cannula hub 34 so that each cannula tab 37 seats in a separatesyringe groove 99. Syringe 90 is then rotated. Owing to the seating ofcannula tabs 37 in syringe grooves 99, this rotation drives syringe head96 into cannula bore 50. Owing to the dimensioning of the components,syringe head 96 presses against the inner wall of the hub that definesmiddle bore 50 as seen in FIG. 6. Owing to the nature of the materialforming the components, this action results in the slight expansion ofthe cannula hub and/or the syringe head. The flexure of either or bothof these components 34 and 96 forms an annular seal around the interfacebetween these components.

By pressing the plunger 102 distally forward, the anesthetic is forcedout through the distal end opening in the cannula tube 60. Theanesthetic blocks the transmission of neurological signals, includingpain signals, that can be generated in the next step. The syringe 90 isthen removed. The syringe removal process is a reverse of the syringecoupling process.

To perform the actual nerve ablation, the electrode 70 is again coupledto the cannula. The same process used to couple and lock the electrode70 to perform the stimulation procedure is used to lock the electrode inplace at the start of the ablation procedure. Again current is sourcefrom/sunk to the end of the electrode shaft 80 that is located forwardof cannula tube 60. This time the current sourced/sunk is at a higherlevel, typically between 400 and 700 mAmps. The resistance of the tissueto this current heats the nerve to the level where the cell forming thenerve ablates.

The electrode 70 is then withdrawn from the cannula. Cannula 32 isremoved from the patient.

Assembly 30 of this invention is constructed so that when the electrodeassembly is coupled to the cannula, the distal movement of the electrodeis blocked by the abutment of the assembly head 74 against step 46internal to the cannula. The dimensions of a single set of componentsforming the assembly are constant. This means that each time theelectrode array is inserted in the same cannula the distal end 81 of theelectrode shaft 80 projects essentially the same distance forward fromthe distal end of the cannula tube 60. This means that between theseparate steps of the procedure, the stimulating step and the ablationstep, even though the electrode assembly is removed and then reinsertedinto the cannula, assuming the position of the cannula is static, theposition of the exposed end of the electrode shaft 80 likewise does notchange. This invention minimizes the likelihood that that, due tovariations in the positioning of the electrode head 74 in the cannulahub 34, the position of the exposed distal end of the electrode shaft 80likewise shift. Using this assembly 30, while maintaining the cannula 32in a fixed position, means that the tissue targeted for ablation duringthe stimulating procedure is the tissue to which the ablating current isthen applied.

Still another feature of this invention is that owing to thedimensioning of the components essentially minimal force, essentially azero insertion force, is employed to insert the electrode 70 in thecannula 32 and to remove the electrode from the cannula. This reducesthe extent to which the forces applied to the cannula 32 to remove theelectrode assembly after the stimulating step and reinsert the electrodeat the beginning of the ablation step can cause unintended movement ofthe cannula.

Likewise the simple rotation of the electrode assembly relative to thecannula moves the electrode between the locked and load states. Thelocking of the electrode 70 to the cannula 32 prevents the unintendeddecoupling of the electrode that could otherwise occur. Again owing tothe design of this invention, only nominal force is applied to thecannula 32 and electrode 70 to move the electrode between the locked andunlocked states.

In addition to the above features, assembly 30 is designed so that whenthe syringe 60 is fitted to the cannula 32, a seal is formed between inthe hub of the cannula around the head of the syringe. This ensures thatthe pressurized fluid, upon discharge from the syringe 90, flows towardsthe target tissue internal to the patient as opposed to leaking out ofthe proximal end of the cannula 32.

When the electrode 70 is fitted to the cannula, fluid may percolatethrough the cannula and lodge in the seat on cannula step 46. Notches 48function as flow paths through which the fluid is able to gravity flowaway from the step 46.

FIG. 7 illustrates an alternative assembly 120 constructed in accordancewith this invention. Assembly 120 includes an alternative cannula 32 aand an alternative electrode 70 a. While not illustrated in FIG. 7, itis understood that assembly 120 includes the previously describedsyringe 90.

Cannula 32 a is substantially identical to the previously describedcannula 32. The difference in the two cannulae 32 and 32 a is thatcannula 32 a does not have the notches 48 incorporated into cannula 32.

Electrode 70 a is essentially identical to electrode 70 a. Thedifference between the electrodes 70 and 70 a is that the proximal todistal length of the head 74 a of electrode 70 a is shorter than thelength of the head of electrode 70. More specifically, electrode 70 a isshaped so that when head 74 a seats in cannula proximal bore 40, thedistally directed face of head does not abut step 46.

Assembly 120 of this invention is thus designed so that when electrode70 a is coupled to cannula 32, the flat distally directed face of trunk73, the face from which head 74 a extends, abuts the proximally directedface of cannula hub main body 36. This is the annular face of thecannula hub that defines the opening into proximal bore 40. The face oftrunk 73 also abuts proximally facing surfaces of the tabs 37 integralwith the cannula hub 34. These surfaces of the cannula hub thus functionas the stop surfaces that block the further advancement of the electrode70 a and, by extension, advancement of the electrode shaft 80.

As with the first assembly of this invention, syringe 90 is inserted inthe cannula hub 34. When this event occurs, syringe head 96 pressesagainst the surface of the hub that defines the middle bore 50 to form aseal between the cannula hub and the middle bore.

A benefit of assembly 120, is that when the practitioner sees theelectrode trunk 73 pressing against the adjacent exposed faces of thecannula hub 34 the practitioner will visual notice that electrode 70 ais in its distalmost position relative to cannula 32 a.

FIG. 8 is illustrates the features of a cannula 136 of still anotherassembly of this invention. Cannula 136 includes a hub 138. Hub 138 hasa main body 139. Tube 60 extends from the distal end of the main body.The hub main body 139 includes a first proximal bore 144 similar to bore40. Proximal to bore 144 there is a first middle bore 150. First middlebore 150 is analogous in shape and function to bore 50. A step 146,similar to step 46 is located between bores 144 and 150. A second middlebore, bore 152, extends distally from bore 150. A constant diameter bore154, similar to previously described bore 54, extends from the secondmiddle bore 152. Bore 154 opens into tube 60.

Cannula hub 138 includes two ribs 142, one rib shown. Ribs 142, whichare analogues to ribs 42, extend from the inner wall of the main bodythat defines the first proximal bore 144 so as to extend into the bore144.

Cannula hub 138 includes a branch 160 that angles away from the mainbody 139 of the hub. In many versions of the invention, the branch 160extends proximally rearward from the section of the hub main body 139 inwhich bore 152 is formed. In many but not all versions of the inventionhub 138 is formed so that the angle between the longitudinal axisthrough the hub main body 139 and the longitudinal axis through branch160 is an acute angle. At the proximal end of branch 160, the branch isshaped to have proximal bore, the second proximal bore 162 of the hub138. Bore 162 is tapered such that extending distally from the proximalend of branch 160 the diameter of the bore 162 decreases. Moreparticularly, the taper of bore 162 is such that the head 96 of syringe90 can press against the inner wall of the hub 138 that defines the bore138. The distal end of bore 162 opens into a transition bore, bore 164.Bore 164 has a taper such that, extending proximally, the diameter ofbore 164 decreases at a greater change in diameter to length ratio thanbore 162. The proximal end of bore 164 opens into a constant diameterconduit 166. Conduit 166 extends through hub branch 160. The distal endof conduit opens into the interior wall of the cannula main body 139that defines bore 152.

Cannula 138 is inserted into the patient using the same methods used toinsert cannulae 32 and 32 a. An electrode 70 or 70 a is inserted throughbores 144, 150 and 152 so as to project out of the cannula tube 60. Theengagement of the cannula ribs 142 with the electrode ears 76 removablyholds the electrode 70 or 70 a to the cannula. A stimulating current issourced through the electrode 70 or 70 a to find the nerve that is to besubjected to the ablation procedure.

Once the targeted tissue is located. The practitioner inserts thesyringe 90 in second proximal bore 162. Owing to the cannula hub havingtwo proximal bores 144 and 160, the practitioner does not have to removethe electrode 70 or 70 a in order to couple the syringe to the cannula136.

During the injection of the anesthetic into the tissue, some of theanesthetic may flow into, in order bores 152, 150 and 144. During thisphase of the procedure, the electrode ears 76 and cannula ribs 142continue to cooperate to releasably hold the electrode 70 or 70 a to thecannula 136. Accordingly, there is essentially no likelihood that thefluid pressure of the anesthetic in the bores 144, 150 and 152 actingagainst the electrode 70 or 70 a will cause the electrode to moverelative to the cannula 136.

Cannula 136 of this invention thus allows the practitioner to introducean anesthetic into the tissue to which the ablating current is to beapplied without having to remove and the reattach the electrode to thecannula. This can reduce the time it takes to perform the procedure.Also since the electrode 70 or 70 a is not removed between thestimulating step and the tissue ablation step, the likelihood the tip ofthe electrode will shift position relative to the cannula 136 betweenthese two steps is further reduced.

The above is directed to specific versions of the assembly forsequentially applying an electrode to and introduce a fluid to a sitelocated percutaneously within the patient. Other versions of thisassembly may have features different from what has been described. Thusthe features of the different versions of the invention can be combined.

For example, the cannula and electrode may have alternativecomplementary features for releasably holding the electrode in theproximal bore 40. One such set of features includes providing the one orboth the cannula or electrode with a J-shaped slot. If the cannula 32 isprovided with this slot/slots, the slot/slots is/are formed to projectoutwardly from the inner wall 39 of the cannula that defines bore 50.Thus the slot/slots is/are a recess/recesses in the inner wall of thecannula hub. The other component is provided with a tab/tabs that seatin the slot/slots. The insertion of the electrode seats the tab/tabs/inthe slot/slots. Once the electrode 70 is seated, the electrode isrotated to seat the tab/tabs in the outer end of the slot/slots. Thisrotation thus places the electrode in the locked state relative to thecannula. An advantage of this version of the invention is that itensures that when the electrode is locked in the cannula the shaft 80 isin a specific rotational orientation relative to the cannula tube 60.This may have benefits material to a specific use of the assembly ofthis invention.

Similarly the locking features integral with the cannula that protrudeoutwardly into the cannula bore 40 may have geometries different thanthose of the depicted ribs. For example the locking features may be aset of ramps and stops that protrude into the cannula bore. Theelectrode is formed with one or more complementary tabs. As aconsequence of the electrode head being inserted in the cannula proximalbore 40, the abutment of the tabs against the cannula ramps and stopscause the rotation of the electrode head.

The outer shape of the cannula 32 is understood to not be a part of thepresent invention.

Further, there is no requirement that the cannula be formed so that step46 is aligned on a plane perpendicular to the longitudinal axis thatextends through the cannula. In other versions of the invention, thisstep may be a tapered step. This taper may be such that, extendingdistally through the hub, the diameter of the step decreases.Alternatively, this step may be such that extending proximally throughthe hub the diameter of the step decreases. In this version of theinvention, step thus forms an annular void space that is locatedimmediately forward of the outer perimeter of the electrode head 74.Generally, it should be understood that step 46 is a surface that isangularly offset from the adjacent proximal surface internal to the hubthat defines the adjacent distal end of proximal bore 40. Step 46, inaddition to being angularly offset from this surface is located radiallyinwardly from this adjacent proximal surface. Further, the surfaceforming step 46 is angularly offset from the adjacent distal surfacethat defines the adjacent proximal end of distal bore 50. Step 46, inaddition to being angularly offset from this bore 50-defining surface islocated radially outwardly from this surface.

In the preferred versions of the invention, step 46 is a surface that,relative to a line that is parallel to the longitudinal axis of thecannula and that extends proximally from outer edge of the step, is atan angle that is a maximum of 90° from this line.

In some versions of the invention, it may be desirable to seat acompressible washer on hub step 46. In these versions of the invention,essentially zero insertion force is used to initially seat the electrodehead 74 in the cannula proximal bore 40. The complementary lockingcomponents are arranged so that the rotation of the electrode to performthe locking process drives the electrode head 74 against washer. Thisresults in a compression of the washer so the washer functions as a sealbetween the cannula and the electrode. In this version of the invention,the ears 76 of the electrode head would thus be compressed between thewasher and the complementary component of the cannula hub, for example,the ribs 42.

The dimensions, unless recited in the claims, are offered for purposesof specific applications of the invention.

Further, the described assembly is shown as being part of a conventionalmonopolar radiofrequency ablation system. The cannula and complementaryelectrode of this invention may have other shapes. For example, theApplicant's PCT Pat. App. No. PCT/US2013/027038, TISSUE ABLATION CANNULAAND ELECTRODE ASSEMBLY THAT CAN BE SELECTIVELY OPERATED WITH ONE OR MOREACTIVE TIPS, filed 21 Feb. 2013, published as WO 2014/130031 A1, thecontents of which are explicitly incorporated herein by reference,discloses the benefits of curving the cannula tube and electrode shaft.These features can be incorporated into the present application.

Likewise, there is no requirement that assembly only be used as part ofa monopolar radiofrequency assembly. An alternative assembly of thisinvention may include a cannula and electrode designed to function aspart of a bipolar radiofrequency assembly. In this type of assembly thecannula tube is formed to have a conductive surface that is separatefrom the conductive surface of the exposed tip of the electrode shaft.This is often accomplished by forming the tube as a set of overlappingtubes. The Applicant's PCT Pub. No. WO 2006/119245/U.S. Pat. No.7,918,852, the contents of which are explicitly incorporated herein byreference, discloses one such design. Conductors extend from thissurface back to the console over which the current is sourced. When thissystem is activated, the sourced current flows between the exposed tipof the electrode shaft and the exposed conductor integral with thecannula.

There is no requirement that in all versions of the invention, thecannula hub may be a single piece component. In some versions of theinvention, the cannula hub 34 and tube 60 may be a single piececomponent.

Likewise, in alternative versions of the invention, a feature other thancannula may be formed with a feature other than step 46 that functionsas a stop that prevents further advancement of the electrode. Thusfeature may, for example, be a ring that protrudes into the proximalbore formed in the cannula. The ring may be formed of material that isflexible. Thus, when head of the electrode that presents a relativelylarge surface area to the ring, the resistance the ring imposes to thefurther insertion of the electrode functions as the tactile feedbackthat the practitioner should stop inserting the electrode. When asyringe, with a tapered nose, is inserted into the cannula. The surfacearea and taper of the syringe collectively causes the practitioner toemploy a less force in order to overcome the resistance of the ring. Inthese versions of the invention the ring thus forms are seal between thecannula and the syringe.

In the above-described version of the invention, the proximally directedface of the ring is the equivalent of the step internal to the cannulahub. The ring surface that extends distally from this proximally facingsurface defines the bore in which the head of the syringe is seated.

Likewise, there is no requirement that in all versions of the inventionthe cannula proximal bore, the bore in which the electrode head 74 isinserted by cylindrical in shape. In cross section the bore may benon-circular. In length, the diameter of the bore may vary along thelongitudinal axis.

In some versions of the invention the bore immediately contiguous withproximal bore 40 may not be the bore dimensioned to receive head 96integral with syringe 90. Thus, in some versions of the invention theproximal portion of the first middle bore 50, the section of the middlebare that partially defines step 46 may have a diameter that is constantalong the proximal to distal longitudinal axis through the bore. In someversions of this invention this constant diameter middle bore 50 mayhave features designed to cooperate with complementary features integralwith the syringe that facilitate the sealing and/or holding of thesyringe to the cannula.

In versions of the invention with two proximal bores, the middle boreadjacent the proximal bore dimensioned to receive the electrode 70 or 70a may not be dimensioned to receive the head of the syringe 90. In theseversions of the invention, the two proximal bores 144 and 162 may beparallel.

It is therefore the object of the appended claims to cover all suchmodifications that come within the true spirit and scope of thisinvention.

What is claimed is:
 1. A cannula for performing an electrosurgicalprocedure with an electrode and a syringe, said cannula comprising: ahub, said hub being formed with a through path that extends betweenopposed proximal and distal ends of the hub, the through path beingdefined by: a first inner surface of said hub that defines a proximalbore that has a constant diameter and that is dimensioned to receive anelectrode head; and a second inner surface of said hub that defines amiddle bore adjacent the proximal bore, the middle bore having adiameter, that is dimensioned to receive a syringe head and that,extending distally from the proximal bore decreases in diameter so thatthe middle bore has a taper so that the syringe head will abut thesecond inner surface of said hub; and a locking feature that extendsoutwardly from or protrudes into the proximal bore, said locking featureconfigured to cooperate with a complementary locking feature of theelectrode head, so that when the locking features engage, the electrodehead is releasably held in the proximal bore of said hub; and a tubethat extends forward of the distal end of the hub, said tube having alumen through which, when the electrode head is seated in the proximalbore of said hub, a shaft of the electrode extends into the lumen ofsaid tube.
 2. The cannula of claim 1, wherein the cannula hub lockingfeature is a rib that extends inwardly from the proximal bore-definingfirst inner surface of said hub into the proximal bore.
 3. The cannulaof claim 1, wherein said hub is formed to define a step that extendsinwardly from a distal end of the proximal bore so as to function as atransition surface between the proximal bore and the middle bore.
 4. Thecannula of claim 3, wherein said hub is further formed so that step is:angularly offset from the adjacent first inner surface of said hub andextends radially inwardly from the first inner surface is adjacentproximal surface; and angularly offset from second inner surface of saidhub and is located radially outwardly from the second inner surface. 5.The cannula of claim 4, wherein said hub is further formed so that saidstep is a surface that, relative to a line that is parallel to alongitudinal axis of the cannula and that extends proximally from anouter edge of said step, is at an angle that is a maximum of 90° fromthe line.
 6. The cannula of claim 3, wherein the cannula hub is furtherformed so that said step is disposed in a plane that is perpendicular toa longitudinal axis of the through path through said hub.
 7. The cannulaof claim 3, wherein said hub is further shaped so that: the middle boreis defined by a circumferential wall internal to the hub; and at leastone notch extends inwardly from bore defining inner wall, the at leastone notch intersecting and interrupting said step between the proximalbore and the middle bore.
 8. The cannula of claim 3, wherein said hub(34) is shaped so that difference in diameters between the adjacentportions of the proximal bore and the middle bore that define,respectively, outer and inner perimeters of said step is at least 0.2mm.
 9. The cannula of claim 1, wherein said tube has a maximum outerdiameter of 2.0 mm.
 10. The cannula of claim 1, wherein said hub isshaped so that the middle bore adjacent the proximal bore anddimensioned to receive the syringe head (96) is a first middle bore (50)and distal to and contiguous to the first middle bore said hub is formedto have a second middle bore that is part of the through path throughsaid hub and said hub is shaped so the second middle bore have a taperthat, extending distally from the first middle bore (50), is morepronounced than the taper of the first middle bore (50).
 11. A cannulafor performing an electrosurgical procedure with an electrode and asyringe, said cannula comprising: a hub, said hub being formed with athrough path that extends between opposed proximal and distal ends ofthe hub, the through path including a proximal bore that is formed insaid hub and that is dimensioned to receive a head of the electrodehead), and a middle bore formed in said hub adjacent the proximal bore,the middle bore having a diameter less than the diameter of an adjacentsection of the proximal bore so that, internal to the hub, a step (46)extends inwardly from the inner surface of the hub that defines a distalend of the proximal bore, said step dimensioned to function as a stopthat prevents advancement of the electrode head beyond the step; and,distal to the step, the through path through the hub is formed to have asection shaped to receive the syringe head and, said hub is furtherformed to have a locking feature that is associated with an innersurface of the hub that defines the proximal bore, said locking featureconfigured to cooperate with a complementary locking feature of theelectrode head, so that when the locking features engage, the electrodehead is releasably held in the cannula hub; and a tube that extendsforward of the distal end of the hub, said tube having a lumen in which,when the electrode head is seated in said hub, a shaft of the electrode(70) extends;
 12. The cannula of claim 11, wherein said hub is furtherformed so that said step is: angularly offset from the adjacent proximalsurface internal to the hub that defines the adjacent distal end ofproximal bore and is located radially inwardly from this adjacentproximal surface; and angularly offset from the adjacent distal surfacethat defines the adjacent proximal end of middle bore and is locatedradially outwardly from this surface.
 13. The cannula of claim 11,wherein said hub is further formed so that said step is a surface that,relative to a line that is parallel to the longitudinal axis of thecannula and that extends proximally from an outer edge of said step, isat an angle that is a maximum of 90° from this line.
 14. The cannula ofclaim 11, wherein said hub is further formed so that said step (46) isdisposed in a plane that is perpendicular to a longitudinal axis of thethrough path through said hub.
 15. The cannula of claim 11, wherein saidhub is further formed so that the middle bore is the portion of the ofthe though path through the hub that is dimensioned to receive thesyringe head.
 16. The cannula of claim 11, wherein the cannula hublocking feature is a rib that extends inwardly from the bore-defininginner surface of said hub.
 17. The cannula of claim 11, wherein said hubis formed so that the proximal bore has a diameter that is constantalong the length of the bore.
 18. The cannula of claim 11, wherein saidhub is further shaped so that: the middle bore is defined by acircumferential wall internal to the hub; and at least one notch extendsinwardly from bore defining inner wall, the at least one notchintersecting and interrupting said step between the bores.
 19. Thecannula of claim 11, wherein said tube has a maximum outer diameter of2.0 mm.
 20. The cannula of claim 11, wherein said hub is shaped so thatdifference in diameters between the adjacent portions of the proximalbore and the middle bore that define said step is at least 0.2 mm. 21.The cannula of claim 11, wherein said hub is shaped so that, distal tosaid step, the middle bore has a diameter that is constant along thebore.
 22. The cannula of claim 11, wherein said hub is shaped so thatmiddle bore that defines said step is a first middle bore and distal toand contiguous to the first middle bore, there is a second middle bore,the second middle bore shaped so as to have a taper that extendsinwardly and that, extending distally from the first middle bore, ismore pronounced than the taper of the first middle bore.